"Invisible" SeaWorld: Evidence of Titan Mimas possessing an interior ocean was discovered

A scientist at the Southwest Research Institute (SwRI) set out to prove that Saturn's moon Mimas is a frozen inert moon, but found convincing evidence that Mimas has an internal ocean of liquids. In the final days of NASA's Cassini mission, the spacecraft spotted a strange balance, or oscillation, in the rotation of the satellite, which typically points to a geologically active body capable of supporting the oceans inside.

"If Mimas had oceans, it would represent a new class of small ' invisible' ocean worlds whose surfaces would not expose the presence of oceans," said Dr Alyssa Rhoden of SwRI, who studies those that contain oceans, as well as the evolution of giant planet satellite systems.

One of the most profound discoveries of planetary science over the past 25 years has been that in our solar system, it is common for worlds with oceans under rocks and ice. Such a world includes giant planets with icy moons such as Europa, Titan and Enceladus, as well as distant planets like Pluto. A world with surface oceans like Earth must be located within a narrow distance from stars to maintain the temperature that supports the liquid ocean. However, the Inner Water Ocean Worlds (IWOWs) were discovered over a much larger range, greatly expanding the number of habitable worlds that could exist throughout the Galaxy.

Rhoden said: "Since Mimas has a serious crater on the surface, we think it's just a piece of frozen ice. IWOWs, such as Enceladus and Europa, tend to be fractured and show signs of other geological activity. It turns out that the surface of Mimas is deceiving us, and our new understanding greatly expands the definition of a potentially habitable world in our solar system and beyond. ”

Tidal processes dissipate the energy of orbit and rotation in the form of heat in the satellite. To match the internal structure extrapolated from Mimas's balance movements, the tidal heating of the moon's interior must be large enough to keep the ocean from freezing, but small enough to sustain a thick ice shell. Using tidal heating models, the team developed numerical methods that create the most plausible explanation for steady-state ice crusts 14 to 20 miles thick on liquid oceans.

"Most of the time, when we create these models, we have to fine-tune them to produce what we're observing," Rhoden said. "This time the evidence for the inner ocean simply jumps out of the most realistic ice crust stability schemes and observed scales."

The team also found that heat flow from the surface is very sensitive to the thickness of the ice crust, something that spacecraft can verify. For example, the Juno spacecraft plans to fly through Europa and use its microwave radiometer to measure the heat flow of the Europa satellite. The data will allow scientists to understand how heat streams affect the ocean world's ice crusts, such as Mimas, which is of particular interest as NASA's Europa Clipper approaches launch in 2024.

Rhoden said: "While our results support the existence of an ocean within Mimas, it is challenging to reconcile the orbital and geological features of this satellite with our current understanding of its thermal orbit evolution." Assessing Mimas' status as an ocean satellite will provide a baseline for models of its formation and evolution. This will help us better understand the ubiquity of Saturn's rings and medium-sized moons, as well as potentially habitable ocean moons, especially on Uranus. Mimas is a compelling target for continued investigation. ”